Method of preventing stress corrosion in a bellows expansion joint

ABSTRACT

A novel bellows expansion joint design and method of preventing stress corrosion cracking incorporates an internal cylindrical weir or sleeve which defines an inner flushing chamber adjacent the expansion bellows wherein connections are provided on the exterior wall of the expansion joint body to allow the admission of a chemical solution or treating fluid directly onto the inside surface of the bellows from an external connection to the expansion joint. In addition, a further connection is provided to a second flushing chamber surrounding the exterior of the bellows so that a similar solution may be admitted and allowed to overflow from an upper portion of the chamber.

This is a division of application Ser. No. 520,433, filed Aug. 4, 1983now U.S. Pat. No. 4,576,404.

BACKGROUND OF THE INVENTION

In various processes, including petroleum and petrochemical processing,metallic bellows expansion joints are utilized to absorb relativemovement in piping and conduit systems. The specific alloy utilized forthe bellows depends on the service environment encountered in theparticular process unit. In many cases, austenitic type steels andstainless steels are required due to the combination of elevatedtemperatures and corrosive elements in the process fluid. Theseaustenitic steels and stainless steels are subject to metallurigalattack known as stress corrosion cracking under certain conditions. Insome cases, such stress corrosion cracking is caused by the presence ofcertain types of acid-forming compounds such as hydrogen sulfide beingpresent in the process stream and therefore on the bellows steel. Forexpansion joints operating at high temperatures, conditions conducivefor the initiation of stress corrosion cracking often exist only duringa shut-down of the process unit when the expansion bellows cool fromtheir high operating temperature down to ambient temperature. Expansionjoint bellows are particularly vulnerable to this type of failure due tothe extremely high stress levels present in the bellows during such downtime and the relatively thin material employed in bellows fabrication.

In practice, it has been found that the actual attack and initialcracking of a stainless steel metal bellows occurs only after thestainless steel has been sensitized, so to speak, by having been heatedto a high elevated temperature and then cooled, and is then attacked bysome kind of acid. A family of weak acids is formed on the stainlesssteel by combination of water and oxygen from the air and almost anysulfur compound, or product of sulfur corrosion, from the chemicalprocess, when the metal bellows are cooled. When the acid forms on thesensitized metal, cracks will occur in the metal.

One way of combatting this phenomenon in the past upon unit shut-downhas been to spray, or attempt to spray, a chemical solution through theexpansion joint external shroud seal openings in order to try to flushthe outside of the expansion bellows to neutralize any acid that mayform on the exterior surface of said bellows. Attempts have also beenmade to spray a neutralizing solution on the interior surface of theconduit in an attempt also to flush the inner walls of the bellows.These attempts have proved difficult in application, or impossible, dueto the configuration of the surrounding parts in the conduit to protectthe bellows from direct exposure to the elevated temperatures of theprocess fluid. In addition, access to the internal surface of thebellows must be obtained from inside the expansion joint, and the timedelay in gaining this access can be sufficiently long so as to permitcracking before such access is obtained. After exposure to the heatedprocess conditions, this stress corrosion cracking can occur in a veryshort period of time after shut-down of the unit, and experience hasshown that expansion joint failures will occur when proper treatment isnot provided within hours of unit shut-down.

It has also been found that if such precautions are not taken for theprompt protection and flushing of an expansion bellows immediately afterunit shut-down, the likelihood of stress corrosion cracks appearing isgreatly increased but they will often be found only upon restart of theunit, at which time, when the failure is found, the unit must be againwithdrawn from service at great cost and expense merely to replace thefailed expansion joint.

SUMMARY OF THE INVENTION

Accordingly, the novel and new bellows expansion joint design of thisinvention and method of preventing stress corrosion cracking thereinprovides a solution to the foregoing problem and incorporates aninternal cylindrical weir or sleeve which defines an inner flushingchamber adjacent the expansion bellows wherein connections are providedon the exterior wall of the expansion joint body to allow the admissionof a chemical solution or treating fluid directly onto the insidesurface of the bellows from an external connection to the expansionjoint. In addition, a further connection is provided to a secondflushing chamber surrounding the exterior of the bellows so that asimilar solution may be admitted and allowed to overflow from an upperportion of the chamber.

The novel structure of the invention permits a novel method to bepracticed for preventing stress corrosion cracking of the expansionbellows in conduits which have been exposed to elevated temperatures andhave hydrogen sulfide or other acid-forming compounds present uponcooldown of the bellows. This method includes the steps of introducing aneutralizing solution into a first chamber interior of the bellows andsimultaneously introducing a similar solution into a second chamberexterior of the bellows, all from the outside of the conduit member. Thenovel method permitted by the structure of the invention allows theintroduction of the necessary neutralizing solutions promptly, eitherduring cooldown of the conduit or immediately afterward, therebyeliminating any long time delays previously experienced in attempting tointroduce the same types of neutralizing solutions to the interior andexterior surfaces of conventional expansion bellows employed in similaroperating environments. Ordinarily, solution introduction willpreferably be started as soon as possible after the bellows andsurrounding conduit structure have cooled below 212° F.

Similarly, the invention contemplates an improved expansion jointconfiguration for use in a high temperature gas conduit wherein an innercylindrical sleeve is provided adjacent the inner surface of the bellowsto form a chamber contiguous therewith so that a neutralizing solutionmay be introduced from a connection means on the exterior surface of theexpansion joint so that said solution may be readily introduced into theinterior surface of the bellows upon cooldown thereof from the elevatedoperating temperature of the expansion joint. The novel structuralarrangement also contemplates a similar solution-containing chamberexterior of the bellows so that concurrently with the introduction ofsolution to the interior of the bellows a similar solution may beintroduced to completely wash the bellows' exterior surface.

Accordingly, it is an object of the present invention to provide a newand novel method for protecting bellows expansion joints from stresscorrosion cracking upon cooldown from elevated surface temperature toambient temperature when said bellows have been operated in a hightemperature environment in the presence of acid-forming compounds suchas hydrogen sulfide.

A further object of the invention is to provide a new and novel bellowsexpansion joint design wherein fluid treating chambers accessible froman exterior surface of the expansion joint are provided on both theinside wall of the bellows as well as on the outside wall of thebellows.

A still further object of the invention is to provide an improvedbellows expansion joint design which is simple and rugged inconstruction, economical to manufacture, and reliable in service.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the nature of the invention, referenceshould be made to the accompanying drawings in which:

FIG. 1 is a vertical cross-section of a bellows expansion joint inaccordance with one form of the invention; and

FIG. 2 is a partial vertical cross-section of an alternate embodiment ofthe invention.

It will be understood that the drawings illustrate merely two preferredembodiments of the invention and that other embodiments are contemplatedwithin the scope of the claims hereinafter set forth.

DETAILED DESCRIPTION OF THE INVENTION

Referring to FIG. 1, an expansion joint 10 in accordance with theinvention is installed in a vertical and downward flowing gas conduit.The expansion joint 10 includes an upper conduit wall section 12 and alower conduit wall section 14. Both of these conduit wall sections 12and 14 are provided with a suitable refractory insulation lining 16secured thereto by a plurality of conventional anchor members 18.Although not specifically illustrated, it will be understood that therefractory insulation 16 will generally be of a dual layer type whereinthe innermost surface is a hard refractory wear layer and the outerportion thereof, closest to the conduit wall, will be a less densehigher insulating capacity material. The upper conduit wall section 12includes an annular flange member 21 to which is welded a dependingcylindrical skirt 20. Skirt 20 includes a lower annular flange member 22and also includes insulation anchor members 24 and a layer of internalinsulation lining 26.

The lower conduit wall section 14 includes an annular flange 28 whichsupports an inner cylindrical sleeve member 30. The flange 28 alsoincludes an outer cylindrical sleeve member 32 which, in cooperationwith the sleeve 30, defines an annular cylindrical cavity therebetweenfor containing a ceramic fiber insulation blanket, such as Kaowool,designated 34.

The expansion joint in accordance with the invention includes a flexiblecylindrical bellows 36 secured at its upper and lower ends,respectively, to the upper conduit wall portion 12 and the lower conduit14. While applicant in describing his expansion joint assembly hasreferred to adjacent conduit walls 12 and 14, it will be understood thatthe expansion joint assembly is normally provided with short sections ofconduit wall integral therewith with suitable flanges or end connections(not shown) for weldable connection directly to the main conduit of theprocess unit in which the expansion joint is to be used. In practice,the expansion joint will be provided by a vendor as an assembly with theappropriate operating diameter for subsequent integral installation intothe associated process piping.

Also secured to the lower conduit wall section 14 is an external jacket"L" shaped member or shroud 38 which extends upwardly to a rim portionlevel with or slightly above the upper end of the bellows 36 and itsattachment point to the conduit 12. The arrangement of the shroud 38defines an outer chamber 52 for containing a solution in contact withthe exterior of the bellows 36. The upper portion of this chamber 52 isenclosed by a cover or shield 40 weldably attached to the conduit 12which cover or shield 40 also includes a downwardly depending lip whoseedge overlaps the upper edge of the shroud 38 to define a solutionoverflow opening 44. Also provided in the lower half of the expansionjoint assembly are two solution inlet conduits 46 and 50 communicatingrespectively with the lower portions of the outer solution chamber 52and the inner solution chamber 48. As can be seen from the drawing, theupper edge of the cylindrical sleeve 32 is disposed slightly above theoutlet opening of the overflow conduit 54 so that solution entering thechamber 48 through conduit 46 will overflow through conduit 54 ratherthan rise above the rim of the jacket 32 and damage the ceramic fiberinsulation 34. Each of the inlet conduits 46 and 50 and outlet conduit54 is provided with a suitable shut-off or drain valve 56.

In operation, the bellows expansion joint of the present invention wouldnormally be free of any liquid in the inner and outer chambers 48 and 52during the high temperature operating mode of the associated processunit. As shown, the hot gas flow would be in a downward directionthrough the conduit, and the conduit would be arranged in a verticalorientation. Upon shut-down of the associated process unit for whateverreason, either a planned shut-down or an emergency shut-down due to someunforeseen process discontinuance, a gradual cooling of all of thecomponents of the conduit and process unit and associated expansionbellows will occur. While ordinarily, without the expansion joint inaccordance with the invention, a considerable time delay would beassociated with any attempt to enter into the interior of the conduit inorder to solution wash the inside surface of the bellows 36, thearrangement of the invention is such that solution such as a mildlycaustic soda ash solution or any other basic neutralizing solution maybe introduced at any desired time after unit shut-down through theconduits 50 and 46 to flood the chambers 48 and 52. While this would notordinarily be done when the metallic parts are still at their highelevated temperatures which might be sufficient to subject thesemetallic parts to thermal shock, the solution may be introduced as soonas the temperature drop is sufficient to allow the safe introduction ofthe neutralizing solutions. This would normally be as soon as thesurrounding parts have cooled below 212° F. As these chambers areflooded by the rise of their respective liquid levels, the overflowsolution will exit through the conduit 54 from the inner chamber 48 andthrough the overflow weir opening 44 from the exterior chamber 52. Whileit is contemplated that optimized stress corrosion cracking preventionsand purging of the acidic compounds adjacent and on the surface of thebellows may be obtained by circulating a basic or caustic solution, itis also contemplated that a sufficient flow of neutral pH 7 water wouldbe adequate to also accomplish the same desired protection in preventingstress corrosion cracking in the bellows 36. Prior to return of the unitto service, the solutions in the chambers 48 and 52 will be drainedtherefrom through their respective conduits 46 and 50 so that no risk ofvaporizing of these fluids will occur at the elevated operatingtemperature of the unit gases flowing in the main conduit.

Referring to FIG. 2, wherein like elements with similar function to FIG.1 have been designated with like reference numbers, an alternateembodiment of the invention is shown. In this embodiment, unlike theFIG. 1 embodiment, the expansion bellows may be oriented in non-verticalconduit sections and may be successfully flushed without loss ofsolution into the conduit interior.

Specifically, in FIG. 2, an inner seal 60, such as the bellows shown,extends between the upper edge of sleeve 32 and the annular flange 21 toprevent leakage of flushing solution into the conduit interior.Additionally, an outer seal 58, which may be a rubber membrane as shownor of other alternate material, seals the chamber 52 so that dischargeof fluid therefrom may occur through the added conduit 54 and valve 56.In this fashion the FIG. 2 embodiment expansion joint may readily belocated in horizontal or inclined conduits to provide quick and positivepurging and neutralizing of any acids that may form on the interior orexterior surfaces of the bellows membrane structure.

While two specific embodiments of the invention have been shown anddescribed in detail to illustrate the application of the inventiveprinciple and method of the invention, it will be understood that theinvention may be embodied otherwise without departing from suchprinciples. For instance, while seal 60 in FIG. 2 has been shown as abellows, those skilled in the art will realize that a packing type sealor a labyrinth seal could be substituted therefor as determined by jointdesign movement and temperatures.

What is claimed is:
 1. The method of preventing stress corrosioncracking upon cooldown of metallic expansion bellows in a conduit whichhas been exposed to elevated temperatures in the presence of sulfurcompounds comprising the steps of:introducing an acid neutralizing basicsolution into a first chamber to contact and wet the inner surface ofsaid bellows; introducing an acid neutralizing solution into a secondchamber to contact and wet the outer surface of said bellows; andmaintaining said solution in said first and second chambers duringcooldown of said bellows and conduit from said elevated temperature. 2.The method of claim 1 including the step of continuously flowing theacid neutralizing solution through said first and second chambers duringcooldown.
 3. The method of claim 2 including the step of draining theacid neutralizing solution from said first and second chambers prior toreturn of said bellows and conduit to elevated temperature service. 4.The method of preventing stress corrosion cracking upon cooldown ofstainless steel expansion bellows in a gas carrying conduit which hasbeen exposed to elevated temperatures in the presence of an acid formingcompounds in said conduit comprising the steps of:introducing a washsolution selected from the group consisting of water and alkalinesolutions into a first chamber to contact and wet the inner surface ofsaid bellows; introducing a wash solution into a second chamber tocontact and wet the outer surface of said bellows; and maintaining saidsolution in said first and second chambers during cooldown of saidbellows and conduit from said elevated temperature.
 5. The method ofclaim 4 including the step of continuously flowing the wash solutionthrough said first and second chambers during cooldown.
 6. The method ofclaim 5 including the step of draining the wash solution from said firstand second chambers prior to return of said bellows and conduit toelevated temperature service.
 7. The method of claim 6 wherein said washsolution is an alkaline solution of soda ash.